1. Field of the Invention
The present invention pertains generally to the field of devices used for adjusting the position of the back rest in a recliner seat and more particularly is directed to an improved hydraulic positioner which is continuously self-compensating for variations in hydraulic fluid volume and visually indicates the amount of hydraulic fluid remaining in a reserve space before servicing or replacement of the unit is required.
2. State of the Prior Art
Hydraulic positioners have long been used in recliner seats where the relative position of the back rest can be fixed at a continuously adjustable angle between an upright and a reclined position. Such devices have found particularly wide application in airline passenger seating. The basic hydraulic positioner of this type has a cylinder with a piston chamber filled with a hydraulic fluid, a piston reciprocable in the chamber, and a piston rod fixed to the piston and extending through one end of the cylinder. The cylinder is fixed to the stationary bottom of the recliner seat, while the free end of the piston rod is fixed to the pivotable back rest of the recliner seat. A valve in the piston allows flow of the hydraulic fluid across the piston, but the valve is normally closed, locking the piston in place relative to the cylinder and fixing the back rest at a given position relative to the stationary bottom of the seat. If readjustment of the back rest position is desired, the valve of the hydraulic positioner is opened by means of a release actuator, such as described in U.S. Pat. No. 4,515,034 issued to this applicant, allowing fluid flow across the piston which is now free to move. After the recliner is brought to the new position, the actuating mechanism is released, returning the valve to its normal, closed position, again locking the back rest of the seat.
Existing hydraulic positioners work well and are used successfully in their intended applications, notably passenger aircraft seating. Wider application of these positioners, for example, to ground transport seating, makes desirable certain improvements. In normal use of the positioner hydraulic fluid is gradually lost over the service life of the device. In certain prior art positioners, a reserve volume of fluid is provided for replenishing the amount lost from a reservoir. An example of a prior art hydraulic positioner is described in U.S. Pat. No. 3,860,098, commonly owned with this application, where a bleed hole under a movable seal is exposed only in full extension of the positioner to replenish the piston chamber with fluid from the reservoir. Full extension occurs when the seat back is brought fully upright. To ensure regular replenishment, the seat backs in airliners are pushed to a fully upright condition between flights as part of an interior "dress-up" routine.
Compensation for thermal expansion and contraction of the hydraulic fluid is specially significant in ground transport applications, where hydraulic positioners may be subject to a very wide thermal range, varying with the local climate and the seasons. Contraction of the hydraulic fluid exposed to cold temperatures can create a vacuum space in the piston chamber which in turn allows a degree of free movement to the piston. Conventional hydraulic locks compensate for this condition when the seat back is brought upright. Failure to do so, however, results in a floppy condition of the seat back with the hydraulic positioner locked. It is also desirable to continuously compensate for the change in effective piston chamber volume which occurs as the piston rod moves in and out of the chamber during the stroke of the piston. As the rod is withdrawn, the effective volume of the piston chamber increases by the volume of the rod segment withdrawn from the chamber. This condition can also create a vacuum space in the piston chamber, which unless compensated by replenishment from a reservoir of hydraulic fluid, may likewise creates a floppy condition of the seat back. These characteristics of prior art devices have no significant impact, however, in applications where professional maintenance crews regularly and frequently return the seat backs to a vertical condition, and where the operating temperature range is relatively limited. Owners of private vehicles, on the other hand, cannot be relied upon to return the seat to a fully upright position with any regularity to replenish fluid lost from the piston chamber.
Hydraulic positioners are used in passenger seats on commercial airliners, where the back rest of the passenger seat is movable between a fully upright position and a more comfortable reclining position. The maximum permissible reclining angle of the back rest for a particular seat depends, among other factors, on the spacing between successive seat rows in an aircraft as well as the location of a particular seat within the aircraft. Seats adjacent to an aircraft exit, for example, may require limitation of the maximum depression of the back rest to assure adequate clearance at all times for safe passage. Seats of similar design in a particular aircraft may therefore require different limits to the recliner adjustment depending on the location on a particular seat in the aircraft. Similar considerations may apply to recliner seat installations in other vehicles, such as automotive applications. In the usual installation, an external coil spring of substantial size is mounted coaxially with the cylinder and compressed between the cylinder and rod, biasing the device to an extended position which usually corresponds to a fully upright position of the recliner back rest. The seat occupant repositions the back rest by first actuating the valve to an open position and then pushing backwards on the back rest to drive the rod into the cylinder against the bias of the external spring, then releasing the valve control to its normal, closed position, to lock the seat back rest at the selected new angle. The positioner is consequently adjustable through a stroke of the rod relative to the cylinder, between a fully extended and a retracted condition. In order to limit the maximum angle of depression of the recliner back rest, it is necessary to limit movement of the rod into the cylinder to stop the stroke short of the fully retracted condition otherwise possible in the particular positioner.
In the past, such limitation has called for use of customized mechanical stops in such positioners, dimensioned to meet the requirements of each particular seat installation.
U.S. Pat. No. 5,133,245 commonly owned with this application, discloses a continuously adjustable stroke limiter attachment which can be readily fitted onto hydraulic positioners requiring such a stroke limiter.
It is desirable however, to provide the self-compensating positioner, as well as other hydraulic positioners of this general type, with a continuously adjustable stroke limiter which is integrated with the positioner, rather than a retrofit or optional add-on.